Death Finds a Way: A Janie Riley Mystery by Lorine McGinnis Schulze. Janie Riley is an avid genealogist with a habit of stumbling on to dead bodies. She and her husband head to Salt Lake City Utah to research Janie's elusive 4th great-grandmother. But her search into the past leads her to a dark secret.
A: The most abundant isotope of magnesium has 12 neutrons; it is therefore, technically known as magnesium-24. Calculating the number of neutrons in an isotope of any element involves subtracting that element's atomic number from its atomic weight. Magnesium's number is 12, and its weight is just over 24.
The idea here is that you need to use the chemical formula for magnesium nitride, #Mg_3N_2#, to calculate the mass of one mole of the compound, i.e. its molar mass. So, magnesium nitride is an ionic compound made up of magnesium cations, #Mg^(2+)#, and nitride anions, #N^(3-)#. The subscripts used in the compound's chemical formula tell you how many ions you get in one formula unit of magnesium nitride. In this case, you have.